It is well known throughout the oil well drilling industry that the rate at which liquid hydrocarbons are recovered from a subsurface formation can be increased by introducing or injecting any of several fluids into the formation. The use of water flooding or steam injection, for example, to stimulate production from a particular subsurface formation is widely known.
According to one technique that has proven particularly effective, a plurality of so-called injection wells are spaced around a producing well. Thus, when fluid is injected into a particular hydrocarbon-containing subsurface formation through each of the several injection wells, the hydrocarbons are driven by the pressure of the injected fluid toward the wellbore of the producing well, from which they are recovered.
It is also well known that a single wellbore may commonly pass through several hydrocarbon-containing subsurface formations. The physical characteristics, such as the depth, porosity, homogeneity, and sand thickness of each such formation may differ, as may the gravity, viscosity, and average molecular weight of the hydrocarbons present in each such formation. Because of these factors, it may be desirable to employ fluid at a particular flow rate, temperature and pressure in stimulating one zone and another combination of flow rate, temperature and pressure in stimulating another treatment zone in the same wellbore.
In the past, flooding or injection has frequently been attempted by perforating the casing in a wellbore at relatively close intervals over a range of depths spanning several producing zones. Pressurized fluid is then introduced into the casing near the top of the perforated range through a single channel conductor or conduit. However, when utilizing this injection method and apparatus, most of the fluid goes into the top few feet of the perforated zone, resulting in an inefficient and undesirable injection profile. Moreover, when a fluid is injected merely by introducing it under pressure into the wellbore, significant conductive heat loss occurs through the casing and well cement, and into the surrounding non-producing strata.
In an effort to overcome difficulties encountered with the foregoing method and apparatus, attempts have been made to control the flow of fluid to different production zones through the use of downhole flow regulators. Such regulators control the rates at which the fluid is released from a single channel conduit to various producing zones. Nevertheless, additional problems have been experienced with this method and apparatus. Monitoring the fluid flow into each zone is still difficult, and a wireline crew is needed in order to service or reposition the regulators.
Therefore, an apparatus and method are needed that will enable those working in the hydrocarbon production industry to more efficiently introduce fluid at different flow rates, temperatures and/or pressures to separate treatment zones within a single wellbore.